assume cs:code
code segment
main:
mov ax,0020h
mov ds,ax ;指定段地址0200h
mov dx,0h
mov cx,003fh
s:
mov [dx],dx
inc dx
loop s
mov ax,4c00h
int 21h
code ends
end main

原因:16 Bit CPU中,不能用DX间接寻址,必须用BX、BP、SI、DI